1. Field of the Invention
The present invention relates to a heat exchanger for use as a condenser and a radiator of an air conditioner for a vehicle etc., and methods for manufacturing the heat exchanger.
2. Description of the Prior Art
FIGS. 17-22 show a typical conventional heat exchanger which requires the heat exchange between a heat medium (for example, cooling medium) flowing in the heat exchanger and air passing through the heat exchanger. A heat exchanger 1 shown in FIG. 17 comprises a pair of header pipes 2 extending in parallel relation to each other, a plurality of heat-transfer tubes 3 disposed between the header pipes and connected to the header pipes at their end portions, a plurality of radiation fins 4 provided on the sides of the heat-transfer tubes, and a pair of reinforcement members 5 disposed on the top and bottom radiation fins. An inlet tube 6 for introducing the heat medium into heat exchanger 1 is connected to one of header pipes 2, and an outlet tube 7 for delivering the heat medium out from heat exchanger 1 is connected to the other header pipe.
Heat-transfer tube 3 is formed as a straight flat tube, which is flattened in the horizontal direction, as shown in FIGS. 18 and 20. A wave-shaped plate 9 is provided in the flat tube 3 to form a plurality of flow paths in the flat tube, as shown in FIGS. 20 and 21. Alternatively, the plurality of flow paths may be formed by partitions 10 as shown in FIG. 23. To support flat tubes 3, connection holes 8 are formed on the surfaces of header pipes 2 with a predetermined pitch such that the respective holes extend in the same direction as the flattened direction of flat tubes 3. The end portions of each flat tube 3 are inserted into the corresponding connection holes 8, and fixed to header pipes 2.
However, since header pipe 2 of heat exchanger 1 (FIG. 17) has connection holes 8 extending in the direction perpendicular to the axis of the header pipe and into which flat tubes 3 having a uniform-sized cross section are inserted, the pipe for constituting the header pipe must have a diameter greater than the width of flat tubes 3 in the longitudinal direction of the cross section of the flat tubes. Therefore, the content volume of header pipes 2, which does not directly contribute to the heat exchange, becomes large, and thereby increases the amount of the used heat medium.
Moreover, when the end portions of flat tubes 3 are inserted into connection holes 8 of header pipes 2 and the flat tubes are positioned relative to the header pipes in the assembly of the heat exchanger, it takes a fairly long time to make the lengths of the end portions of the flat tubes inserted into the connection holes uniform, and assembly is not easy.
Further, the wave-shaped plate 9 having the same length as that of flat tube 3 is inserted into the flat tube. The portions of the wave-shaped plate that contact with or approach the inside surface of the flat tube are welded onto the inside surface of the flat tube by, for example, brazing in the step of making the flat tube 3 with wave-shaped plate 9 therein (for example, the method disclosed in unexamined Japanese Patent Publication SHO 62-175588). However, it is difficult to uniformly weld the relatively long wave-shaped plate 9 in the flat tube 3. If wave-shaped plate 9 is not formed as a desired shape which is adapted to the inside form of flat tube 3, a plurality of flow paths separated from one another cannot be formed. This failure makes it difficult to increase the efficiency of the heat exchange by uniformly diverging the flow of the heat medium into a plurality of flow paths and passing the heat medium uniformly through flow paths which are separated from one another. Furthermore, since wave-shaped plate 9 must be preformed so that it is adapted to the inside of flat tube 3 before it is inserted, the processing and preforming of the wave-shaped plate is a troublesome operation.